1. Field of the Invention
The present invention generally relates to well completion. More specifically, the invention relates to placement of downhole tools in a wellbore using logging equipment run into the wellbore on a tubular string with the tools. Still more particularly, the invention relates to the use of wireless, real time communication between logging components run into well on a tubular string and the surface of the well.
2. Description of the Related Art
Hydrocarbon wells are formed by drilling an initial borehole in the earth and then lining the borehole with pipe or casing to form a wellbore. The casing prevents the walls of the wellbore from caving in and facilitates the isolation of certain parts of the wellbore. Subsequently, at least one area of the wellbore casing is perforated to permit communication with an oil bearing formation therearound. As the oil enters the perforated casing, it is typically collected in a separate tubular string used as a conduit to move the oil to the surface of the well.
In one example of well completion, a borehole is formed and casing is then run into the borehole. The casing is initially suspended from the surface of the well but is thereafter cemented into place with cement deposited in the annular area formed between the outer surface of the casing and the walls of the borehole. In order to access a formation of interest around the wellbore, a bridge plug may be installed in the wellbore below the area of interest. The bridge plug is run into the well on a tubular string and includes an outward radially extendable sealing element to contact and seal an area between the bridge plug and the casing wall. Bridge plugs can be set hydraulically or mechanically and their use is well known in the art. With the bridge plug set, a tubular string with a packer, a screened portion and a perforating gun are run into the well. When the perforating gun is adjacent the formation of interest, the packer is set. Packers, like bridge plugs include a radially extendable sealing element. Additionally, packers include a central bore with a sealing member therein to seal the area between the inner bore and the production tubing extending therethough. With the packer set and the area of the wellbore isolated, the perforating guns are fired and the casing and cement therearound are perforated. With the perforation, fluid communication is established between the formation fluids and the surface of the well via the production tubing. Additionally, the producing area of the wellbore is isolated from other areas.
The foregoing example is simplified. More typically, various areas of a wellbore are isolated and perforated in order to access different formations that are present at different depths in the wellbore. More importantly, lateral wellbores are now routinely formed from a central wellbore to reach and to follow formations extending from the central wellbore. The lateral wellbores are drilled from the central wellbore and are initiated with the use of a whipstock or some other diverter that can be run into the wellbore in a tubular string and anchored therein. The whipstock includes a slanted or concave area which can guide a cutting tool though the wall of the casing to form a “window” though which a lateral wellbore can be formed. In other instances, casing is run into the central wellbore with a preformed window therein. With the window in place, a new borehole can be formed and with directional drilling techniques, the new wellbore can reach or follow a particular sand or other hydrocarbon bearing formation.
Prior to the well completion techniques described above, wellbores are routinely the subject of a variety of testing designed to determine the characteristics of surrounding formations. The characteristics are indicative of the types of fluids present in formations. One type of testing is performed with a gamma ray tool. A gamma ray tool includes a radiation detector for detecting naturally occurring gamma radiation from a formation. An electrical signal is produced corresponding to each detected gamma ray and the signal has an amplitude representative of the energy of the gamma ray. The detector includes a scintillation crystal or scintillator which is optically coupled to a photomultiplier tube. The scintillator may comprise a gadolinium-containing material, such as gadolinium orthosilicate that is suitably doped, for example with cerium, to activate for use as a scintillator. The quantity of cerium in terms of number of atoms is typically of the order of about 0.1% to about 1% of the quantity of gadolinium. The scintillator may comprise other materials, such as sodium iodide doped with thalium (NaI)(Tl), bismuth germanate, cesium iodide, and other materials.
Another type of logging tool is a neutron tool. Neutron tools are used to analyze fluids in a formation to determine their characteristics. This is especially important where water or some other non-hydrocarbon fluid has migrated into an area adjacent a perforated wellbore. Production of water creates additional expense and necessarily reduces the production of oil at the surface of the well. In order to identify and eliminate water entering a wellbore, the formations around the wellbore are tested using a logging tool such as a neutron tool. The neutron tool emits neutrons into the formation and subsequently recovers the neutrons after they have been deflected by the formation. By counting the number of neutrons returning, the makeup of the fluid can be determined and water, oil and gas can be identified and distinguished. Thereafter, elimination packers can be installed in the wellbore to contain the water. The neutron tool is conventionally run into a well on wireline and the isolation packers are subsequently run in on a tubular string to a location corresponding to the depth at which the logging tool indicated the presence of water.
In the examples above, tubular strings with tools are inserted into a wellbore and lowered to a position of interest based upon previously measured information related to depth and information about formations and fluids therein. The previous measurements are typically performed in an open hole with the logging tools conveyed on wireline. However, during the subsequent process of conveying the tools with tubing or drill-pipe, improper or inaccurate measurements of the length of the drill string may take place due to inconsistent lengths of collars and drill-pipes, pipe stretch, pipe tabulation errors, etc., resulting in erroneous placement of the tools. Thus, the tools may be positioned in the wrong area of the wellbore and the surrounding formations may not be effectively accessed. Repeating the insertion of the tool string may be very costly both in expenses and time.
There is a need therefore, for a method and apparatus to combine some aspects of well logging with some aspect of well completion. There is a further need for methods and apparatus to utilize well logging and downhole tools in a single trip. There is yet a further need for methods and apparatus permitting downhole well completion tools to logged into a wellbore on a run-in string of tubulars along with logging tools to ensure that the downhole tools are positioned at the optimum location in the wellbore. There is yet a further need for methods and apparatus to locate wellbore completion tools in a cased wellbore that more completely utilizes logging data from prior, open hole tests. There is yet a further need for apparatus and methods that includes the run-in of various downhole tools along with various logging tools capable of operating in a cased wellbore in order to locate a zone of interest in real time and place the tools in the optimum place in the wellbore in a single run with no separate power lines extending from the apparatus to the surface of the well.